Evaluation of the Copepod Eurytemora affinis Life History Response to Temperature and Salinity Increases

Abstract

Zooplankton and particularly copepods have a key role in the functioning of aquatic ecosystems. However, the mechanisms involved in the physiological responses of copepods to temperature and salinity increases are little understood, and the role of plasticity involved in facing environmental changes has rarely been demonstrated experimentally. In this study, the copepod Eurytemora affinis, widely distributed in the northern hemisphere, was selected as a biological model to test the effect of a 4 degrees C temperature increase at two salinities. In addition to the optimal salinity (15 psu), a stressful condition of salinity 25 psu was also verified. Copepods from the Seine estuary were acclimated in laboratory to their optimal temperature of 15 degrees C at salinity 15 PSU and then they were acclimated during several generations to their upper thermal limit (20 degrees C) at two salinities (15 and 25 PSU), after which the temperature was raised by 4 degrees C. This experiment revealed that after long-term acclimation and under unlimited food conditions, E. affinis maintained good fitness at 20 degrees C and at both optimal and stressful salinities. After temperature increase to 24 degrees C, the population remained viable but copepod size was significantly decreased as well as female's fecundity. The decrease of fitness was accentuated under the additional stressful condition of salinity 25 psu. This study demonstrated that the mechanisms of response to temperature and salinity increases (i.e. global warming) are complex, and should be investigated through experimental studies that consider acclimation and multigenerational factors. Our results will enrich the development of Individual-Based Models (IBMs) capable to test the role of microevolution and plasticity of E. affinis in the framework of future climate scenarios.